69 C10 SWB big block, buckets - $19K.
If this is how you'd want to build one, you probably couldn't do it for this price. I don't THINK this has been posted already, but it's been on CL for a while now.
https://dallas.craigslist.org/dal/ct...416348257.html
72 C20 Cheyenne Super, big block, a/c (I think). $2500
https://sanantonio.craigslist.org/ct...419848588.html